I grouped these ones together because they have long bodies and predominately black with black legs. Did one just nab that bee by using its butt? This one didn't do alot of flying - it crawled around over and under leaves and flowers.
In this family of flower wasps only the male is winged and he is much larger than the female. Coupling is extended and the male flies with the female attached. In your photo, she has access to a flower which she otherwise would not have been able to get to